Fuel cells electrochemically oxidize hydrogen to generate electric power. Without a hydrogen refueling infrastructure, hydrogen has to be produced from available fuels at the point of use. In remote, distributed, and portable power applications, such fuel cell systems require small, lightweight fuel processors that are designed for frequent start ups and are capable of operating at varying loads.
Two processes are industrially used to generate hydrogen from hydrocarbon fuels. These two processes include the steam reforming process and the partial oxidation reforming process. The steam reforming hydrogen production process is the more commonly used process used to produce hydrogen. This is especially true in the chemical industry. Steam reforming is an endothermic reaction that is typically slow to start up. In steam reforming processes, steam reacts with a hydrocarbon fuel in the presence of a catalyst to produce hydrogen. In steam reforming, the process equipment tends to be heavy and is designed for continuous operation under steady state conditions making such systems unsuitable for applications with frequent load variations such as those for use in transportation applications. Additionally, because of the endothermic nature of the process, steam reforming reactors are heat transfer limited. These attributes of steam reforming processes makes them unsuitable for use in remote, distributed, and portable power applications such as for use in a motor vehicles.
Partial oxidation reforming processes are based on exothermic reactions in which some fuel is directly combusted. In partial oxidation reforming, oxygen reacts with a hydrocarbon fuel in the presence of a catalyst to produce hydrogen. Heat transfer limitations are eliminated in partial oxidation reforming processes due to the exothermic nature of the reaction. Additionally, partial oxidation reforming hydrogen production processes and the equipment used in such processes generally allows for faster start ups compared to steam reforming processes. However, reactors used in partial oxidation reforming processes generally operate at temperatures of from about 1100° C. to about 1200° C. to prevent coking in the reactor. One disadvantage associated with partial oxidation reforming is that reactor materials capable of operating at the high temperatures of partial oxidation processes must be used. Suitable materials for use in partial oxidation reforming reactors include ceramics. Ceramic reforming reactors are both expensive and difficult to fabricate.
U.S. Pat. No. 5,248,566 issued to Kumar et al. discloses a fuel cell system for use in transportation applications. In the disclosed fuel cell, a partial oxidation reformer is connected to a fuel tank and to a fuel cell. The partial oxidation reformer produces hydrogen-containing gas by partially oxidizing and reforming the fuel with water and air in the presence of an oxidizing catalyst and a reforming catalyst.
U.S. Pat. No. 6,025,403 issued to Marler et al. discloses a process for integrating an autothermal reforming unit and a cogeneration power plant in which the reforming unit has two communicating fluid beds. The first fluid bed is a reformer reactor containing inorganic metal oxide and which is used to react oxygen and light hydrocarbons at conditions sufficient to produce a mixture of synthesis gas, hydrogen, carbon monoxide, and carbon dioxide. The second fluid bed is a combustor-regenerator which receives spent inorganic metal oxide from the first fluid bed and which provides heat to the inorganic metal and balance the reaction endotherm, by combusting fuel gas in direct contact with the inorganic metal oxide producing hot flue gas. In preferred embodiments, steam is also fed to the reformer reactor and a catalyst may be used with the inorganic metal oxide.
U.S. Pat. No. 6,126,908 issued to Clawson et al. and WO 98/08771 disclose an apparatus and method for converting hydrocarbon fuel or an alcohol into hydrogen gas and carbon dioxide. The apparatus includes a first vessel having a partial oxidation reaction zone and a separate steam reforming reaction zone that is distinct from the partial oxidation reaction zone. The first vessel of the apparatus has a first vessel inlet at the partial oxidation reaction zone and a first vessel outlet at the steam reforming zone. The reformer also includes a helical tube that has a first end connected to an oxygen-containing source and a second end connected to the first vessel at the partial oxidation reaction zone. Oxygen gas from an oxygen-containing source can be directed through the helical tube to the first vessel. The apparatus includes a second vessel with both an inlet and outlet. The second vessel is annularly disposed about the first vessel, and the helical tube is disposed between the first vessel and the second vessel and gases from the first vessel can be directed through the second vessel. The temperature in the partial oxidation zone within the apparatus is preferably maintained in the range of from about 950° C. to about 1150° C.
WO 00/66487 discloses an autothermal reforming system with a reformer reactor, integrated shift beds, preferential oxidation reactor, auxiliary reactor, and system controls. The reformer reactor of the autothermal reforming system is similar to that disclosed in U.S. Pat. No. 6,126,908 issued to Clawson et al. and WO 98/08771 in that it has distinct and separate partial oxidation, steam reforming, low temperature shift, and high temperature shift zones. The exothermic reaction in the partial oxidation chamber is self-sustaining and maintains an operating temperature in the range of from about 700° C. to about 1,200° C. for an embodiment of a catalyzed partial oxidation chamber or at a temperature of from about 1,200° C. to about 1,700° C. for an embodiment that uses a non-catalyzed partial oxidation zone.
U.S. Pat. No. 5,458,857 issued to Collins et al. discloses a combined reformer and shift apparatus. The combined reformer and shift reactor comprises a cylindrical reforming chamber arranged within and on the axis of a cylindrical vessel. An annular steam generator is arranged within, and coaxially with the vessel. The steam generator is arranged around the reforming chamber. A plurality of shift reactors extend axially, with respect to the vessel through, through the steam generator. Methane and steam are supplied via helically coiled pipe to the reforming chamber and air is supplied via helically coiled pipe. The methane and steam mixture and air flowing through the pipes are preheated by the reforming chamber product gases flowing in annular passage. The methane is preheated to prevent quenching of the steam in the disclosed apparatus and method of operation. The normal operating temperature in the reforming chamber is 700° C. to 1200° C. and the low temperature shift reactors are operated at a temperature between 140° C. and 250° C.
U.S. Pat. No. 5,861,137 issued to Edlund discloses a steam reformer with internal hydrogen purification that include internal bulk hydrogen purification, internal hydrogen polishing to remove trace levels of carbon monoxide and carbon dioxide, an integrated combustion method utilizing waste gas to heat the reformer, efficient integration of heat transfer, and compact design. The steam reformer includes a concentric cylindrical architecture nesting an annular combustion region, an annular reforming region separate from the combustion region, an annular hydrogen transport region, and a cylindrical polishing region. Thus, the reforming apparatus disclosed is similar to other conventional apparatus in having distinct and separate chambers for partial oxidation and steam reforming.
A need remains for a fuel processor that optimizes the production of hydrogen in autothermal reforming processes such that the fuel processor can be manufactured from conventional materials.